The invention relates to drawing-type dies in general and more particularly related to die means for folding at least one edge of a tape to overlie the main central portion thereof.
So-called folded tape shields have been used for many years to protect electronic cables from the intrusion of unwanted signals. A tape of this kind comprises a thin insulating layer of plastic such as polyester, polypropylene and Teflon. One side of the tape is laminated with a thin conducting layer or foil of metal such as aluminum and copper. Preferably, both of the tape edges are folded inward in directions such that the foil of one edge is exposed and the plastic of the other edge is exposed. Typically, the shield is formed by spiral wrapping the tape around a group of insulation covered conductors in a manner such that the metal exposed folded edge surface makes good electrical contact with the conducting layer of the tape's main central portion. Folding of the other edge to produce a fold having an exposed insulating film assures that the exposed edge of the tape does not have an edge of raw metal.
While the merits of folded tape shields have been virtually undisputed, the relatively high cost of tape folding tools has severely limited the production of such shields. That is, folding tool costs have been relatively high because of inherently expensive constructions and the fact that the prior art folding tools were usually constructed so that they were not adjustable for different tape widths and were not adustable to produce different widths for the folded over edges. Further, prior art tape folding tools were constructed of metal which developed relatively high friction forces as the tape moved through the forming openings of the tools. These friction forces generated heat and drag on the tape resulting in uncontrolled stretching of the tape and, in many cases, reducing the useful fatigue life thereof after the folded tape shields were placed in service. This undesirable friction also resulted in abrasion of the metal faces of the tape shields.